Gasification of hydrocarbonaceous material, such as coal, shale, lignite or oil sands, usually involves reaction of ground particles of such material with steam at high pressures. Oxygen may be added to provide the endothermic heat of reaction for steam decomposition by partial oxidation of the hydrocarbon containing material. Generally, the reaction is promoted by catalyst, such as iron-chromia compositions. Efficiency of the reaction is promoted by grinding the coal or shale to particle sizes of less than 4 mesh screen size (4.76 mm), and preferrably less than 8 mesh (2.38 mm). Normally, the material is ground in water to control dust and then at least partially dried. In such condition, the hydrocarbonaceous material is in a fine grain or dust-like form so that interaction with gases in the reactor occurs within a few seconds. Accordingly, free flow into the reactor is essential. For such free flow, at reasonably high feed rates, a charging system is essential because of high pressure (on the order of 5 to 80 atmospheres) in the reactor. Additionally, in gasification of solid and liquid hydrocarbons, hydrogen sulphide, carbon monoxide, as well as desired methane, are produced. All of these gases are air pollutants, if released. Accordingly, an isolation chamber, or lock-box, (frequently multiple stages) must be used for flow between a feed hopper and the reactor chamber. For high flow rates, such lock chambers must be large and be able to withstand the pressure in the reactor. Both requirements increase the cost of such chambers. For these reasons, it has been proposed to use relatively small volume lock-boxes with an expansible chamber provided by a cylinder with a reciprocating piston to vary the pressure in the box. Gates or valves are provided for admitting and withdrawing the ground hydrocarbonaceous material.
Where such finely ground material is mechanically forced into the reactor by a piston either sliding laterally or vertically from below, some agglomeration or compaction results. Material being pressed by the piston is compressed against the balance of the charge. This then requires subsequent recomminution of the compacted particles.
Further, hydrocarbon containing materials, such as coal, shale, lignite and oil sand, generally include rock particles such as quartz, limestones, and clays. These materials are particularly abrasive to pistons, cylinders and sliding gates in typical lock-box constructions of the prior art.
U.S. Pat. No. 3,039,939, Welsh, discloses charging a shale retort from the bottom by a mechanical cylinder and piston arrangement. Raw shale flows downwardly to fill an inclined cylinder. The cylinder then pivots from the inclined, fill position to vertical to mate with a bottom entry port in the reactor. The piston then physically lifts the raw shale in the cylinder so that each new charge of shale displaces a portion of the shale undergoing reaction upwardly within the retort.
U.S. Pat. No. 4,207,081, Preusser, et al., discloses a double-piston pump arrangement for pumping fine grained, or dustlike, coal through a lock-box arrangement from a supply hopper to a reactor or gasifier. The piston includes a central chamber which transports the granular coal horizontally when the piston is actuated between its two horizontal extreme positions, one to admit ground coal to the chamber and one to discharge it into the reactor.
U.S. Pat. No. 3,994,418, Andersson, discloses a similar horizontal feed cylinder having a pair of independently reciprocable pistons therein. Feed material is compressed between the two pistons and charged to a gas generator at an elevated pressure. The space between the two pistons is then closed to prevent reactor gas entrapment between the pistons during return of the pistons to the feed intake position.
U.S. Pat. No. 2,151,514--Heinen discloses a system for conveying solids or liquids either to a high pressure zone from a low pressure zone, or vice versa. A lock box arrangement is formed by a pair of gate valves. The gates are cam operated by a crank shaft which drives a piston rod and a piston reciprocable in a cylinder open to the lock-box. The piston controls the cylinder and lock-box pressure as the gates are opened and closed for transfer of solids or liquids.
U.S. Pat. No. 4,082,366--Duff et al. discloses a similar arrangement for recycling polyurethane foam wherein pieces of foam to be recycled are enclosed in a lock-box formed by a pair of gate valves. The gates are successively closed and opened between a feed line and the reactor. A piston and cylinder arrangement exerts pressure on the foam particles to move them through the gate valve between the lock-box and reactor.
U.S. Pat. No. 2,888,155--Raynier et al. shows an arrangement for introducing edible grains into a pressurized steam reactor for manufacture of puffed cereals (e.g., puffed wheat). In this system a lock-box is formed by a pair of pistons operating in interconnected cylinders. Reciprocation of the pistons relative to each other opens and closes the inlet feed, the lock-box and entry to the reactor in the proper order to permit transfer of the cereal. The wall of one piston and the head of the other piston serve as gates for the lock-box arrangement.
As particularly distinguished from such prior art methods and structures, the present invention contemplates formation of finely ground materials, including abrasive rock particles, by gravity feed into a charging cylinder vertically above a reactor and then compressing a gas volume above the charge. Such compression is applied only in an amount and to an extent sufficient to exceed the pressure in the reactor to actuate an end closure plate extending across the charging cylinder. The charge is thus uniformly pressured without agglomeration of the ground particles and at the same time the piston head need not contact the charge. This substantially avoids scraping or scoring action of the cylinder and piston by particles, and particularly those that may be wedged into the space defined by the cylinder, piston walls and the piston rings. In addition, such a system permits addition of small amounts of water or steam to the charge and along the cylinder walls without significant compaction of the particles. In simplest form, air enters the charging cylinder with the gravity flow of ground material. It is then compressed by the piston to create the necessary pressure in the cylinder to actuate the pressure responsive closure means.
A preferred manner of practicing the method of the invention includes introduction of a gas "blanket" between the compressing piston and the charge from an external source such as, oxygen, nitrogen or combustion gas. However, if desired, a "bleed" line from the reactor may be opened to supply such gas above the charge after the cylinder is sealed by the piston. In the latter method, contamination of the reaction product by nitrogen is reduced.
Also in accordance with the preferred method, the gravity feed hopper is closed prior to application of pressure to the charging chamber to permit refilling of the hopper while a charge is being transferred to the reactor in the charging cylinder. Desirably but not necessarily, the top of the feed hopper may also be closed off to prevent back flow of fines due to even a low back pressure in the feed hopper.
Further objects and advantages of the invention will become apparent from the following detailed description of preferred steps and means for carrying out the methods and apparatus of the present invention.